ba is just a cycle that printouts the whole file content after the PATTERN till the end. and note, that those 6 lines are just one command, but newline is needed to delimit the next sed command after
additional info from
info sed :
If auto-print is not disabled, print the pattern space, then,
regardless, replace the pattern space with the next line of input.
If there is no more input then `sed' exits without processing any
[No addresses allowed.]
Specify the location of LABEL for branch commands. In all other
respects, a no-op.
Unconditionally branch to LABEL. The LABEL may be omitted, in
which case the next cycle is started.